1. Field of the Invention
The present invention relates to control circuits, and more particularly to a multiplexer printed circuit board for performing address interrogation for multiple devices under computer control.
2. Description of Prior Art
In tests of compressors and turbines, simultaneous measurements of many steady-state pressures are required. In past years Scanivalves, a registered trademark for a mechanical pneumatic selector switch manufactured by Scanivalve Corporation, have been used for this purpose. A plurality of Scanivalves are incorporated into a data logging system which outputs data on paper tape.
The Scanivalve (S/V) is a device having multiple pneumatic input ports and a single pressure-measuring transducer. A mechanical rotor driven by an electric motor pneumatically connects one input port at a time to the transducer, with the rotor position being controlled electronically. The transducer output is a voltage which after proper conditioning can be measured using a precision voltmeter, and through calibration interpreted as pressure. Operation of the S/V involves address interrogation, position control and transducer measurement. Address interrogation is the identification of the S/V port address; position control is the positioning of the S/V to the specified input port; and transducer measurement is the transforming and sampling of the electrical output of the pressure transducer.
To provide on-line data acquisition to a computer, replacing the data logging system, a S/V control device compatible with the computer system is required to permit acquisition of steady-state data from multiple S/Vs under manual or computer control. The device should be compatible with the IEEE Standard 488-1975, "Digital Interface for Programmable Instrumentation".